Why no diesel Prius?

[roflwaffle]

Originally Posted by Christ

Thanks for the link to the paper. Saved that one.

Unfortunately, the maps shown in that paper reference an increase in emissions when road speed and load are increased steadily, which should be obvious.

What I'm referring to is steady state RPM with varying loads. In other words, when you're cruising, and you start going up a hill, then going down the other side.

Sure they do. Look at the map for NO. At 1500rpm and 2bar, NO is at 100+ppm. Hold speed the same and increase the load to 5bar, NO emissions increase to 200ppm. Emissions increase w/ both engine load and engine speed.

Originally Posted by Christ

If you're not using all the available power, you're pretty much wasting fuel. You can tell if you're properly loading your diesel engine by checking EGT's though. You should be in the ~600* range for best efficiency in most cases, IIRC.

That's not necessarily true. Generally, as long as an engine is above half load it operates pretty efficiently, however at maximum load efficiency tends to drop slightly compared to at high, but not maximum, load.

Originally Posted by Christ

The thing about diesels is that it's hard to control load without metering airflow, so it would be very difficult to test for emissions properly. When you floor it in a diesel, it starts injecting fuel based on a pre-set pump that was supposedly tuned.

All diesels do a great job at governing fuel, and load, not airflow. Even very old designs only use an intake throttle to generate vacuum, which the IP uses to govern fuel and load. The full load screw allows the operator to increase or decrease the amount of full load fuel injected depending on oxygen content, which depends on pressure and humidity mostly.